Sunbathing is a popular activity worldwide. A suntan is associated with health, beauty, status and wealth. Many leisure-time activities, such as swimming, tennis, golf, and fishing, are done in the sun. Furthermore, many people are forced to be in the sun for long periods of time due to their occupation.
However, the damaging effects of sunlight on skin are well documented. Contrary to what most people believe, it is not necessary that one sunbathe to suffer the ill-effects of excessive UV exposure. In fact, a lot of damage can be done just by routine day-to-day activities in the sunlight. Some scientists estimate that over 70 percent of the damage the sun inflicts on the average person's skin over a lifetime is the result of simply being outdoors or even sitting by a window.
The major short term hazard of prolonged exposure to sunlight is erythema (i.e., sunburn). The 290 to 320 nanometer wavelength ultraviolet radiation range, designated as the "UVB" wavelength range, tends to be the primary cause of erythema. The 320 to 400 nanometer wavelength ultraviolet radiation range, designated as the "UVA" wavelength range, also produces erythema.
In addition to the short term hazard of erythema, there are also long term hazards associated with UV radiation exposure. One of these long term hazards is malignant changes in the skin surface. Numerous epidemiologic studies demonstrate a strong relationship between sunlight exposure and human skin cancer. Another long term hazard of ultraviolet radiation is premature aging of the skin. This condition is characterized by wrinkling and yellowing of the skin, along with other physical changes such as crackling, telangiectasis (spider vessels), solar keratoses (growths), ecchymoses (subcutaneous hemorrhagic lesions), and loss of elasticity (sagging). The adverse effects associated with exposure to UVA and UVB wavelength radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonpresciption Drugs, 7th Ed, Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C.; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, DePolo, issued June 7, 1983; the disclosures of all of which are incorporated herein by reference. Hence, although the immediate effects of ultraviolet radiation may be cosmetically and socially gratifying, the long-term hazards are cumulative and potentially serious.
The fact that these effects are taken seriously by the general public is suggested by considering the sun protection products' market. This market has grown considerably in recent years and many new products are introduced each year. What used to be looked upon as a seasonal business is no longer. Sun protection compounds are now included in a diversity of personal care products, particularly cosmetic-type products which are worn on a daily basis.
Obviously the most effective way to avoid excessive UV exposure is to simply refrain from being out in the sun. This is not only an impractical solution but an impossible one for those who work out-of-doors. Furthermore, some effects of exposure to sunlight are beneficial. Vitamin D is synthesized in skin exposed to UV radiation. A deficiency of this vitamin in the body can cause rickets or osteomalacia. Also, recent research suggests that sunlight can alter physical processes in ways that could enhance one's feeling of well-being.
Sunscreening agents exist naturally in the skin. These include melanin, carotenoids, urocanic acid, proteins and lipids. These natural sunscreens do not afford complete protection however, and for persons with very light skin they afford little protection at all.
Over the years, many means have been conceived of to mitigate the effects of UV exposure. In Middle Eastern countries people shield their skin with long robes, kaffiyehs and veils. This is not an acceptable solution for most people however.
Sunblock agents are commercially available to protect the skin from UV radiation. These agents scatter or reflect ultraviolet radiation. Examples include titanium dioxide and zinc oxide. However, compositions containing these agents are opaque, generally unattractive in color, and are viewed as unacceptable for usage on more than just the nose or tops of the ears. Furthermore, these agents are very susceptible to rub-off or wear-off resulting in little or no protection.
Another type of agent available is one which provides a "tan" without exposure to the sun. Such agents generally consist of a skin dye and in no way protect against harmful UV-irradiation. These agents are applied to the skin wherever the appearance of a tan is desired. One example is dihydroxyacetone, which provides color through a reaction with specific amino acids in the stratum corneum. A drawback of this type of product is that it results in uneven coloration and a somewhat unnatural reddish-brown hue.
Related to these products are artifical tanning compounds which are taken orally. One example is canthaxanthin. These compounds apparently work by coloring the fat cells under the epidermal layer. Such products also result in uneven tanning and require continual maintenance doses. Again, these products provide no protection against harmful irradiation.
The most common agents for sun protection are sunscreens. These agents exert their effects through chemical means, i.e., they absorb ultraviolet radiation so that it cannot penetrate the skin. Sunscreens present the user with several problems. For example, they must be on the surface of the skin at the time of exposure to be effective. Sunscreens are preventative so one must anticipate being in the sun. To be most effective, sunscreens must be on the skin as a continuous uniform film. Delivering such a film to the surface of the skin is very difficult; maintaining the film over time is almost impossible. Sunscreens must remain on the surface of the skin during exposure. However, sunscreens are easily rubbed off or washed off by sweating or swimming and can also be lost by penetration into the skin. Sunscreening agents often cause irritation to the skin and eyes, primarily burning or stinging, respectively. Another problem with sunscreens is that the greater their efficacy, the more the tanning response is decreased.
Methods have been suggested for improving the look of skin after the UV-induced damage has occurred. Topical application of collagen as a moisturizing agent is one such method. Others involve injections of collagen or dimethylpolysiloxane. Yet another procedure entails the application of a chemical preparation to the skin to effect a "chemical peel".
Alternatively, methods have been suggested for repairing skin after UV-induced damage has occurred. One such method involves application of retinoic acid to the skin as disclosed in U.S. Pat. No. 4,603,146, Kligman, issued July 29, 1986. None of these procedures have been proven to be fully effective and most involve extensive and costly treatment. Clearly, it would be far better to prevent the damage induced by UV-irradiation before it occurs. A photo-protecting agent which protects against both short-term and long-term UV-damage to the skin while, at the same time, allows for tanning of the skin in a safe, convenient manner would be most ideal.
Conjugated dienoic acids and their derivatives, in general, are known to be useful as quenchers for protecting the skin from harmful effects of UV exposure. For example, the use of a number of compounds, including 2,4-hexadien-1-ol, for controlling the chronic effects of prolonged exposure to sunlight are disclosed in U.S. Pat. No. 4,098,881, Majeti, issued July 4, 1978. The use of sorbic acid or salts thereof in sunscreen formulations is also known. See e.g., U.S. Pat. No. 4,264,581, Kerkhof et al., issued Apr. 28, 1981.
Tocopherol (Vitamin E) has been disclosed for use as a photoprotector in topical compositions. See, e.g., U.S. Pat. No. 4,144,325, Voyt, issued Mar. 13, 1974. Tocopherol works to protect the skin from deleterious effects of UV-irradiation without interfering with the tanning response. However, cosmetic industry experience suggests that tocopherol may have stability problems, specifically oxidation problems. One frequently used approach to address these problems involves the formulation of compositions including esters of tocopherol, these esters generally being more stable than tocopherol itself. U.S. Pat. No. 4,248,861, Schutt, issued Feb. 3, 1981, discloses the use of tocopherol acetate, tocopherol succinate, tocopherol propionate, and tocopherol oleate for preventing deleterious effects to skin of solar radiation. U.S. Pat. No. 4,000,276, Hasunuma et al., issued Dec. 28, 1976, discloses a cosmetic composition comprising tocopherol orotate. Tocopherol benzoate, p-aminobenzoate, and p-nitro-benzoate have been disclosed for use in sunscreen compositions in European Patent Application No. 166,221, Tuominen, published Jan. 2, 1986. The linoleate, nicotinate, and 2-ethylhexanoate esters of tocopherol have been disclosed for use in cosmetic compositions in Japanese Laid-Open Application No. 61-143,331, published Dec. 14, 1984. Increased formulational stability, as provided by most tocopherol esters, unfortunately comes at the cost of decreased photoprotection efficacy. Clearly, a photo-protecting agent which works as well as tocopherol but which is not subject to stability problems would be most desirable.
The topical use of anti-inflammatory agents to alleviate erythema is known. Compositions containing steroidal anti-inflammatories, non-steroidal anti-inflammatories, as well as "natural" anti-inflammatories, such as an extract of the plant Aloe vera, have been disclosed for such use. See e.g., U.S. Pat. No. 4,185,100, Rovee, issued Jan. 22, 1980 (hydrocortisone, dexamethasone, naproxen, ketoprofen, ibuprofen); U.S. Pat. No. 4,338,293, Holick, issued July 5, 1982 (steroidal anti-inflammatories); Law, et al., Br. J. Pharmac., 59(4), 591-597 (1977) (ibuprofen); Kaidbey, J. Invest, Dermatology, 66, 153-156 (1976) (indomethacin); and Gruber, et al., Clinical Pharm. and Therapeut., 13(1), 109-113 (1971) (aspirin, fenoprofen). Short-term application of anti-inflammatory agents prior to UV exposure to prevent erythema, as well as application after UV exposure to lessen UV-induced damage to skin has been taught.
It is an object of the present invention to provide a topical composition in a stable form, the use of which will prevent both acute (erythema) and chronic (photoaging) effects of exposure to the sun.
It is also an object of the present invention to provide a topical composition, a cleansing composition, and a method for preventing these deleterious effects of the sun without interfering with the tanning response.
It is further an object of the present invention to provide a photoprotection composition which penetrates into the skin and which is less susceptible to rub-off, wear-off or wash-off.
It is a still further object of the present invention to provide a photoprotection composition which can be applied to the skin in advance of UV exposure without significant loss of efficacy.